aw os 的基础链表是双向循环链表，这样的好处是插到尾部速度非常快，有些传统的os 采用了单个指针头的双向链表，虽然这样省了4个字节指针，但是算法复杂了，插入到尾部时间不确定，意义不大。-Aw OS based list is a circular doubly linked list, such benefits is inserted into the tail velocity is very fast, some traditional OS uses a single pointer